The present world display devices operate with a distorted (non-linear) input signal to produce an approximately accurate color reproduction when displayed. This is primarily an artifact of the non-linear display distortion effects that characterize most CRT (cathode ray tube) devices. Additionally, there are many distortions and imperfections caused by all of the imaging devices that capture video and image content as well as distortions introduced by source devices that present the content. In an ideal world, the voltage coming from an electronic camera would be directly proportional to the intensity (power) of light in the scene. Also, the light emitted by a CRT would be directly proportional to its input voltage, and so on. However, real-world devices do not behave in this way.
As briefly stated above, video monitors have historically introduced a certain level of color distortion to the received video signal. Additionally, a certain level of distortion introduced by the video capture and processing steps. Thus, in order to display a video signal that accurately reflects the actual images obtained certain corrections are commonly made to the signal input into a display device.
It is well known that CRT displays, almost all photographic film, and many electronic cameras have nonlinear signal-to-light-intensity or intensity-to-signal characteristics. In the industry, most CRT display devices were found to have a level of distortion that is very well approximated using a power function. In one generalized approach, the power function can be described as follows;x=yλ
Where x defines the output signal and y defines the input. The power function γ describes the exponential value used to relate the input and output. The exponent is often called “gamma” and denoted by the Greek letter gamma γ. By convention, input and output are both scaled to the range 0 to 1, with 0 representing, for example, black. Analogously, 1 represents maximum (e.g., white (or red, etc)). Normalized in this way, the power function is completely described by the exponent.
So, given a particular device, the output can be measured as a function of its input. In the industry it is common to refer to a device as having “a gamma of x” which commonly means a device having a power-law response with an exponent of x. Although many devices can have different power functions, it is fairly common in the industry for monitors to have a γ of 2.2 (even digital display devices exhibit the behavior as an artifact of a typical γ for industry standard CRT's). Thus, any signal being displayed by a CRT is distorted by the “display γ”. One particularly common level of such distortion leads to a gamma of about 2.2. This has had an effect on the industry as a whole. In order to correct for the “gamma” distortion introduced by CRT's a complementary distortion is introduced into the input signal, such that when the input signal is displayed, the two effects cancel each other out to produce a display output having generally linear behavior. Due to the commonly occurring and largely uniform distortion occurring a most of the CRT displays made, the industry found it cost effective to introduce a predetermined distortion at the point of content creation rather than conduct γ correction at each display produced. In this way, all of the expensive processing required to correctly color balance a signal is done initially at a small number of locations and thus saves the cost of expensive processing circuitry at each display device.
This situation is far from ideal. First, there are many CRT's that do not display received signal with a gamma of 2.2. This will cause a fair amount of color distortion in the displayed images. In one non-comprehensive example, some devices display at a γ of 1.4. Some displays are more flexible allowing multiple different γ values. However, as an artifact from an older era, a gamma of 2.2 is typically encoded into all color signals distributed as content. This limitation becomes more pronounced when modern display devices are considered. Many of these devices can have virtually any gamma they like as well as very non-linear gamma's. Thus, the need for the legacy 2.2 gamma function is diminishing.
An added problem with this older scheme is that most of this data is typically encoded using 8-bit resolution. This means that for each color channel in a video signal there are 256 separate graduations of intensity. While this is sufficient for most CRT's and many people, the enhanced ability of newer display technologies and the advent of high definition television and its many high resolution analogs, has generated a desire for color signals of higher fidelity. Additionally, signal encoded in with one color format in mind may not “map” very accurately into another format. While existing systems and methods work well for many applications, there is an increasing demand for inexpensive methods and systems that can conduct gamut mapping between two color gamuts to take full advantage of modern multimedia equipment devices (e.g., displays), software and devices. In particular, there is a need for high resolution mapping between color gamuts of various devices. The disclosure addresses some of those needs.